The present invention relates to apparatus and methods for joining together different pieces of materials along a continuous ultrasonically welded seam to form electrical insulators; and to a new and improved insulator for use in dynamoelectric machine stator assemblies.
The manufacture of dynamoelectric machines has developed into a highly sophisticated industry. In the manufacture of wound stators for such machines, coils may be wound on a coil form and then inserted into the stator; or the wire for forming such coils may be directly dispensed into the stat or slots in a so-called "in-slot" winding process. In either approach various insulators are employed in addition to the typical ground insulation that is immediately adjacent to coil accommodating surfaces of the core. For example, an exemplary stator slot may have a cuffed stator slot wedge or slot liner, such as illustrated in U.S. Pat. No. 2,935,859, inserted therein before any wire is deposited in that slot, although slot insulation may also take the form of an epoxy or other resinous coating. With the slot liner in place, a first phase winding may then be inserted in the slot to be followed by a phase insulating wedge or separator. Next, a second winding is inserted in this slot and, lastly, an insulating wedge is inserted in the slot. In this example, where two different phase windings occupy the same slot, it is also desirable to provide additional insulation between the end turns of the two different phases. This additional end turn insulation is sometimes called "window" insulation in the art, and an example of such an approach is shown in U.S. Pat. No. 2,701,317, which was assigned to the assignee of this application. There may also occur connections between different pole windings of the stator and connections from such windings to the stator leads. To insulate such connections, there may be provided additional insulators often in the form of insulators or sleeves such as those disclosed in U.S. Pat. No. 3,219,857 (which is assigned to the assignee of this application), which fit over the interconnected wires and to either side of a particular point of connection. Since these interpole or external lead connections are often soldered, sharp protrusions may be present, and the tubular insulators should be particularly rugged. Stator insulators have at one time or another been manufactured of paper and also of polyester materials, such as polyethylene terephthalate which may be purchased under the trade name "Mylar" polyester. The polyester materials have proven to be particularly desirable materials because of their strength, good electrical insulating properties, and compatibility with lubricants and refrigerants normally encountered in hermetically sealed refrigeration compressor motor parts.
In a hermetically sealed compressor environment, quality of insulation is particularly important since such insulation comes in contact with refrigerant and lubricants employed in the refrigeration system and any insulation failure may result in loss of not only the motor but an entire compressor unit. Any moisture which might be present in the insulators at the time of assembly could of course lead to system damage if that moisture were to subsequently freeze and block the refrigerant circulation path. Because of those considerations such insulators are now almost universally fabricated from synthetic materials, of which polyethylene terephthalate or Mylar polyester will be taken as exemplary throughout the present specification.
While polyethylene terephthalate is particularly suited to the hermetic motor environment, it can be a difficult material to work with and is rather costly. Heating this material in an attempt to bind two pieces of polyester sheet material together results in a thermal degradation of the material which not only weakens the material but also changes its chemical properties somewhat so that the material may be more prone to absorb moisture. Also, if it is overly heated refrigerants such as Freon may later cause a molecular particle to leave the insulator and contaminate the freon base refrigerant. Attempts have been made to bond two sheets of polyethylene terephthalate together by ultrasonic spot welding techniques. However, such welds are not characterized by great strength, and I have found that ultrasonic welding of such material is so detrimental to the ultrasonic welding tips that such tips would rapidly wear away and require replacement. Adhesive or solvent bonding of polyester to polyester is expensive, does not result in particularly strong bonds, and introduces undesirable materials which again may be detrimental in a refrigerant compressor environment.
Present production techniques of, for example, phase insulators is to cut thee insulator from a flat sheet of material and discard almost as much material as is retained for the end turn or phase insulator. The cost of discarding such a substantial quantity of insulating material is of course substantial.
It is accordingly a general object of the present invention to overcome one or more of the foregoing problems.
It is another object of the present invention to provide new and improved electrical insulators from strip insulating material.
A further object of the present invention is to provide a new and improved method for fabricating connection insulators for interpole and winding lead connections in dynamoelectric machines.
A still further object of the present invention is to provide a new and improved and economical phase insulator for dynamoelectric machine stator windings.
Still another object of the present invention is to join polyester materials together without degrading the materials.
A yet further object of the present invention is to effect a substantially continuous polyester material to polyester material ultrasonically welded seam and improved apparatus for use therewith.
It has been recognized in the art that ultrasonic welder tip wear is a substantial problem, and particularly so in connection with welding polyester materials such as polyethylene terephthalate. In fact, the industry makes use of exotic welder tip materials such as titanium alloys, in an effort to reduce welder tip wear. Attempts to harden the tip or portion of the machinery which transmits the ultrasonic vibrations to the material being processed have not been successful, since hardening the vibration transmitting material would substantially diminish its vibration transmitting capabilities. In addition, hard or brittle materials would rupture, crack or break when driven with sufficient energy to ultrasonically weld a work piece.
It is accordingly another specific object of the present invention to overcome the problems associated with wear of an ultrasonic welding tip.
Still another object of the present invention is to provide a wear resistant tip for an ultrasonic device which retain its vibration transmitting efficiency.